FR2550953A1 - PROCESS FOR PRODUCING PERMEABLE MINERAL MEMBRANES - Google Patents

Abstract

THE PROCESS IS CHARACTERIZED IN THAT A THIN LAYER OF A HYDROXIDE GEL AT LEAST OF ALUMINUM PEPTISE IS DEPOSITED ON A PERMEABLE POROUS SUBSTRATE, THE MEMBRANE THUS OBTAINED IS DRIED, THEN IT IS BAKED AT A TEMPERATURE INCLUDED BETWEEN 500C AND 1100C. APPLICATION OF THE MEMBRANES OBTAINED TO ISOTOPIC GAS SEPARATION, FILTRATION AND ULTRAFILTRATION.

Description

The present invention due to the work of René VEYRE, Serge

  RICHARD, Francis PEJOT and André GRANGEON of the Manufacturing Company of Catalytic Elements and Messrs Jean CHARPIN, Pierre PLURIEN and Bernard RASNEUR of the Commissariat 5 for Atomic Energy, is concerned with a process for producing porous and permeable mineral membranes, supported One of the conventional methods for producing this type of membrane consists in depositing on a porous and permeable substrate from a suspension in a liquid of grains or agglomerates of grains of powder, one or more active layers of a single or mixed oxide, then drying, compressing and sintering the assembly thus obtained According to the methods of the prior art, the compression operation is essential; indeed, this compression is necessary to carry out a reorganization of the layer (s) deposited on the substrate of

  so as to obtain a homogeneous microporous texture, not exhibiting macroporosity, and to obtain good mechanical strength by increasing the cohesion within the layer (s) 20 and, optionally, their adhesion to the substrate.

  The method, which is the subject of the invention, makes it possible to obtain porous and permeable mineral membranes, supported by a porous substrate, in a simpler implementation than that described above, in particular in that it is not necessary. The method for manufacturing a porous and permeable mineral membrane, according to the invention, is characterized in that a thin layer of a gel is deposited on a porous permeable substrate. At least one of the peptized aluminum hydroxide is dried, the membrane thus obtained is dried and then subjected to cooking at 500 ° C. to 1100 ° C. According to the invention, the gel used may be either a peptised aluminum hydroxide gel. or a gel of a mixed hydroxide of peptised aluminum capable of forming, after pyrolysis, an aluminum spinel, such as, for example, a mixed hydroxide gel of aluminum and peptised magnesium According to the process of the invention , the hydroxyd gel The peptized aluminum or the mixed gel of aluminum hydroxide and peptized magnesium is deposited on a permeable porous substrate 40 by the so-called engobageo technique. It is recalled that the coating technique applied to the deposition of a suspension of solid particles in a liquid, consists in bringing the inner and / or outer wall of the porous substrate into contact with this suspension capable of forming the layer which it is desired to deposit on the porous substrate. More precisely, this contacting is made by commnunication of the substrate with a tray containing said suspension of solid particles; the tank is provided with a deformable membrane which makes it possible, under the influence of the pressure of a fluid, to generate variations in volume inside the tank, which causes the suspension to rise or fall solid particles along the porous substrate. After drying of the assembly thus obtained, then heat treatment between 500 and 1100 C, a permeable mineral membrane is obtained comprising an active thin layer deposited on a porous substrate, said thin layer being microporous and homogeneous and having a thickness of a few microns and a porous texture of a few tens of Angstroms; The porous and permeable substrates used according to the method of the invention must have a porous ray texture on the surface intended to receive the gel layer. pore less than 2 p, and irregularities of the surface state less than a few microns so as to avoid, respectively significant penetration of the gel in the pores of the substrate, and the formation of cracks or macroporous defects These substrates must in order to exhibit good mechanical strength, high permeability and satisfactory surface finish at the same time, they must consist of a coarse support having pores of high radius (from 4 to

  201 i for example), this support being covered with a thin layer of a few tens of microns having a much finer texture (from 0.05 to 2 pses can be metallic (nickel for example) or ceramic material (in alumina for example).

  The viscosity of the gel used is adjusted so as to

  obtain a suitable wettability of this cel on the subset

  trat; this adjustment of the viscosity can be done either by modifying the concentration of the gel (by diluting it or during its preparation) or by adding a thickening agent to it. The preparation of an aluminum hydroxide gel can, for example, be proceed as follows: starting from an aluminum alkoxide which can be tert-butylate or aluminum isopropoxide; this aluminum alkoxide is hydrolysed with a large excess of water (number of moles H 2 O / number of moles Al close to 100) at a temperature of about 80 C; the hydrated aluminum oxide thus obtained is then peptized, also at a temperature of approximately 80 ° C., in the presence of a strong acid such as hydrochloric acid or perchloric acid for a few hours to three days. A peptized gel, also called a sol (colloidal suspension), is obtained. There are commercially available such aluminum hydroxide sols (boehmite sol). The concentration of this peptized gel, obtained by evaporation, can be adjusted according to The amount desired to be deposited on the porous substrate; the maximum concentration of the gel is obtained for a ratio of

  strong acid / alkoxide concentration of about 0.07.

  This peptised gel of aluminum hydroxide is deposited on a porous substrate having the characteristics given above, for example by the coating technique. The assembly thus obtained is then dried at moderate temperature and then subjected to a heat treatment. The heat treatment has a dual role first of transforming the hydroxide Al (OH) 3 crystallized oxide A 1203, which requires a minimum temperature of about 500 C, then adjust, depending on the application envisaged, the size of the pores by sintering by varying the temperature in the range from 500 ° C. to 1100 ° C. Thus, for a temperature of 500 ° C. for one hour, a microporous layer of alumina of structure Y is obtained. having an average pore radius of about 20 A, and at a temperature of 850 C for one hour, a microporous layer of alumina having an average pore radius of about 40 A is obtained. The porosity is about 62 to 65% O The pe The nitrogen permeability of the membrane thus obtained can vary from 200 to 30000107 mole / cm Hg / cm 2 / min for microporous layer thicknesses varying from 15 to 2 p. The preparation of a mixed hydroxyl ael can be used. to carry out by hydrolysis of an aluminum alkoxide, then addition of a salt of the metal chosen. This metal, which can lead with aluminum to the spinel structure, can be, for example, magnesium, cobalt or copper. In the case of magnesium, it is possible to add, for example, an acetate, an isopropylate, a magnesium perchlorate, previously dissolved in water. The amount of magnesium is pre-measured so as to obtain, after cooking above 800 ° C., a spinel of formula NA 1203, Mg O in which N is greater than or equal to 1. A peptization is then carried out in the presence of a strong acid such as hydrochloric acid or perchloric acid. for a few hours to three 15 days after evaporation n of the colloldale suspension obtained, to concentrate it, a mixed hydroxide sol is obtained which can be filtered through a filter, having pores of about 0.4 p, so as to ensure its perfect homogeneity The peptization of the aluminum hydroxide could also be carried out before the addition of the salt of the other metal. After adjustment of the viscosity of this gel, it is deposited, for example, by the coating technique. the porous and permeable substrate defined above The assembly is then dried at a moderate temperature, then baked at a temperature above 800 ° C. and up to 1100 ° C. The heat treatment also has a double effect: firstly to ensure the transformation of the mixed hydroxide into mixed oxide of spinel structure, which imposes a minimum temperature of 800 ° C., then adjust, depending on the application envisaged, the size of the pores by sintering by varying the temperature in the field

from 800 C to 1100 C.

  Thus, for a firing temperature of 850 ° C. for one hour, the microporous layer thus obtained is of homogeneous spinel structure and has an average pore radius of about 40 Å, and for a cooking temperature of 1000 ° C. for 1 hour. hour, an average pore radius of about 50 A. According to an advantageous embodiment of the process of the invention, it is possible, once the membrane is complete,

'50953

  the deposition of a second layer of peptized gel, which makes it possible to fill any gaps due to a defective wetting during the first deposition operation; this also makes it possible to fill any cracks that may have formed during the firing of the first deposit. The invention will be better understood on reading the

  following description of some examples of implementation

  Of course, these examples have no limiting character with respect to the invention. EXAMPLE I A permeable inorganic membrane is made by defeating a monolayer of a mixed aluminum hydroxide gel and peptized magnesium corresponding to Al / Mg = 6.

  on a porous and permeable substrate This manufacture is carried out as follows.

  We start from a boehmite soil suspended in the water at

g of oxide per liter.

  This solution is diluted to 150% in deionized water and then distilled. An aqueous solution of magnesium acetate is added to this solution in the proportions of boehmite soil parts per 10 parts of a solution.

of magnesium acetate at 81 g / l.

  Two porous substrates a and b in the form of an α-alumina tube are used; they have on their inner surface a primer with average pore radii of either 0.41 or 0.61 (this primer is deposited on a support having a pore radius of 6 p); they correspond bulloscopic unblocking pressures for an air perfusion rate of 120 o 10 3 m Dle / rn, respectively 600 mb and 490 mb, which corresponds to a greater defects amount respectively to 0.81 and 0,961 just measurableo The gel is deposited by the technique of encasing on the

  The inner surface of the substrate is then dried for 15 hours at room temperature and in a humid atmosphere at 60%. It is then baked at 850 ° C. for one hour.

  A membrane having a spinel structure layer 3 A 1203, Mg O is thus obtained, the characteristics of which are given in Table I below.

BOARD

  I Support Characteristics of the support medium radius of the pores of the internal surface of the support Unclogging pressure in bulloscopy alcohol at 120 103 mole / Characteristics of the membrane Permeability radius of the nitrogen pores in (10 7 mole / permeamate 2 m H / trie aacm Hg / cm / min) at 10 bp 0.46 0.66 mb 490 mb 3800 o A> 100 o> 100 A

EXAMPLE II

  A permeable mineral membrane is manufactured by

  depositing a monolayer of a mixed aluminum hydroxide gel and peptized magnesium on a porous and permeable substrate.

  A boehmite sol identical to that initially selected in Example I was used and filtered through a 0.4 "pore size filter. This sol was diluted in 100% water and 50% alcohol. an aqueous solution of magnesium acetate is added in the proportions of 40 parts of soil.

  of boehmite for 10 parts of a solution of magnesium acetate at 81 g / l.

  The porous substrate used is of the type a of Example I. The peptized mixed gel thus obtained is deposited by the coating technique on the inner surface of the support at room temperature. The whole is then dried for 15 hours. at room temperature, in a humid atmosphere t 60%; then

  the whole is cooked at 8500 C for one hour.

  Table II below gives the characteristics of the membrane of homogeneous spinel structure 3 A 1203, Mg O obtained.

T A B L E A U II

  Thickness of permeability to the nitrogen layer (10-7 mol / am Hg / cm 2 / min) pore radius of the layer measured in gas permeametry between 7 bar and 14 bar o 27 A mean pore radius of the porosity layer of the o layer

37 to 63%

800 to 1100

7 2550953

  The membrane obtained, when used for

  gaseous diffusion enrichment of a natural mixture of Argon 36 and Argon 40 has a separation efficiency of 0.749 to 0.722.

EXAMPLE III

  A permeable mineral membrane of spinel 3A 1203, MgO is produced by depositing a peptized gel bilayer

on a porous substrate.

  The membrane made in Example II is taken and a second layer of the same peptized gel is deposited and in the same manner as in Example I Io This layer is then dried and cooked as in Example I Io Table III , below, gives the characteristics

of the membrane thus obtained.

T A B L E A U III

  Nitrogen permeability measured pore radius efficiency (10 7 mole / cm Hg / cm 2 / min) in permeametry ga separation of one zeuse between 7 bars and natural mixture 14 bars of argon

750-20 to 0.755

  It can be seen from the comparison of the data in this table with those in Table II that a membrane with two layers has a lower permeametry and

  separation efficiency of a larger argon mixture.

EXAMPLE IV

  A permeable mineral membrane is manufactured from a

  spinel 3 A 1203, Mg O by depositing a monolayer of a peptized gel on a porous substrate.

  A boehmite sol, identical to that used initially in Examples I to III, is used, and it is filtered on a pore size filter of 0.4 .mu.l. This sol is diluted in% of water. A binder is then added. organic, namely polyvinyl alcohol, in the proportions of 20 to 30% by weight relative to the weight of aluminum oxide. Then an aqueous solution of magnesium acetate of 81 g / l, in the proportions of 40 parts of boehmite sol for 10 parts of magnesium acetate, the peptized gel is evacuated under vacuum in the presence of butanolo

8 2550953

  The porous substrate used is of the type a of Example Io The peptized gel is deposited by the coating technique at room temperature, on the inner surface of the substrate. The assembly thus obtained is dried in an oven at 80 ° C. for three hours, then is cooked up to 600 ° C. with

  rate of rise in temperature of 25 C / h so as to eliminate the organic binder, then at a rate of rise in temperature from 100 C / h to 850 C; it is left at this temperature of 850 C for about one hour.

  Table IV, below, gives the characteristics

  of the spinel structure membrane 3A 1203, Mg O obtained.

T A B L E A U IV

  Thickness of Permeability to nitrogen permeametric ray layer (10 mole / cm Hgcm 2 / n of layer 620 45 A It is seen that by this technique, in which an organic binder is also used, continuous layers are obtained more thick, therefore less permeable, than those

  obtained in the previous examples.

EXAMPLE V

  A permeable mineral membrane of spinel 6A 1203, MgO is produced by depositing a monolayer of a gel

peptized on a porous substrate.

  A boehmite sol identical to that of Examples I to III is used and is filtered on a pore size filter with a mean pore size of 0.4. The sol is then diluted with 50% of water. magnesium acetate at 81 g / l in the proportions of 80 parts of boehmite sol per 10 parts of magnesium acetate

  gel is then degassed under vacuum in the presence of butanol.

  The substrate used is of the type a of Example I. The peptized gel is deposited on the inner surface of the

  substrate by the coating technique, at room temperature.

  The assembly thus obtained is dried in ambient air for twelve hours and baked at 850 ° C. for one hour with a temperature rise rate of 100 ° C / h.

9 2550953

  Table V, below, gives the characteristics of the membrane of homogeneous spinel structure 6 A 1203, Mg O

thus obtained.

T A B L E A U V

  Nitrogen permeability 7 (10 27 mle / cm Hg / cm 2 / m) permeability of the o-layer

1200 60 A

  It can be seen that by adding smaller amounts of magnesium acetate an aluminum spinel n A 1203, Mg O in which N is greater than 3 o can be obtained.

EXAMPLE VI

  A permeable mineral membrane is produced by deposition of a monolayer of a peptone gel of mixed aluminum hydroxide

  and magnesium on a porous and permeable substrate.

  The boehmite sol used in the previous examples is filtered through a 0.4 "mean pore size filter. It is then diluted in 100% water and 50% alcohol.

  An aqueous solution of magnesium acetate at 81 g / l in the proportions of 40 parts of boehmite sol per 10 parts of magnesium acetate is then degassed under vacuum in the presence of butanolo. The alumina tubular substrate The inner surface has a mean pore radius of 500 A. The sol is deposited on the inner surface of the substrate by the coating technique at ambient temperature. The assembly thus obtained is dried in ambient air. for twelve hours and then baked at 850 ° C for one hour with a temperature rise rate of 100 ° C / hr. Table VI, below, gives the characteristics

of the membrane obtained.

TABLE VI

  Permeability to nitrogen permeametric radius separation efficiency (10-7 2 mole / cm Hg / af 2 m of the layer ration of a mixture (10 -7 mole / cm Hg / cm 2 /) of natural argon

700 to 800

At 0.706

2550953

EXAMPLE VII

  A permeable mineral membrane is produced by deposition of a monolayer of a peptised aluminum hydroxide gel

on a porous substrate.

  A boehmite sol at 70 g / l is filtered on a pore size filter of 3 p.

  by evaporation of the water to values of between 150 and 250 g / l. The viscosity of the thus concentrated soil is between 150 and 200 cc. The sol is then degassed under vacuum in the presence of butanol.

  The porous tubular support used is made of α-alumina and has, on the inner surface, an average pore radius of

0.41 '.

  The soil thus concentrated is then deposited on the inner surface of the support by the coating technique at room temperature.

  The assembly thus obtained is dried in ambient air for twelve hours, then is cooked at 600 C with a speed

  rise in temperature of 1000 C / h; it is then maintained at 600 ° C. for one hour.

  Table VII, below, gives the characteristics

  of the alumina structure membrane obtained therein.

T A B L E A U VII

  Thickness of permeability to nitrogen Permeametric layer (10-7 mole / m Hgcm 2 / n) of the layer (10-mole / cm Hg / df 12 / zn) O

at 155 300 40 A

EXAMPLE VIII

  Soil is made using perchlorate

  magnesium as magnesium salt and taking either hydrochloric acid or perchloric acid for peptization.

  Starting from a hydrolysed aluminum secondary butoxide in a reactor, with a large excess of water (100 moles H 2 O per 1 mole of alcoholate) for about 2 hours.

  A quantity of magnesium perchlorate is added

  so as to obtain a molar ratio Al / Mg = 6.

  Then reflux peptization is carried out:

  in the presence of hydrochloric acid with

  2550953 of number of moles of hydrochloric acid number of moles of alcoholic alcohol number of moles to alcohol can vary from 0.09 to 0.15; in the presence of perchloric acid with concentrations of HCl O 4 perchloric acid number of moles H Cl O 4 number of moles alcoholic varying from 0.09 to 0.20 o The peptisation time varies from 2 hours to 4 days,

  Note the clarity of the solution after a few hours of peptization.

  In all cases, the spinel structure 3 A 1203, Mg O was obtained for cooking temperatures ranging from 850 ° C.

at 1000 C for 1 hour.

  Table VIII below summarizes the textures of the samples obtained and measured by the BJH method (Barret, Joyner, Halenda, JACS 73, 373 (1951)) TABLE VIII number of moles H Cl Peptisation in the presence of HCl with number of alcoholic moles = 0.09 mean radius surface specic texture

O 2-1

  cooking 1 h 800 C 35 A 153 m g O 21 850 C 40 A 134 m 2 g 1

14

  1 h 900 C 46 A 117 m 2 g number of moles HC 1 04 Peptization in the presence of HCl O 4 with number of moles alcoholate O '09 mean radius surface specicle texture fique 1 h 800 C 25 A 145 m 2 g 1 to 5 145 mg

O 2 -1

1 h 850 C 25 A 134 mg

90000 28 O 2 -1

1 h 900 C 98 m 2 g -1

O 2 -1

  1 h 1000 C 30.5 to 86 mg Thus, thanks to the process of the invention, after thermal treatment, mircoporous layers very adherent to the substrate are obtained, having no heterogeneity, neither in the thickness nor in the permeametry, and not showing cracks or macropores Depending on temperature and time T

12 2550953

  selected, it is possible to obtain very homogeneous pore radii ranging from 20 to 500 A. The use of the permeable mineral membranes obtained according to the method of the invention is chosen according to their permeability characteristics and the Preferably, the membranes having permeabilities of from 200 to 600 moles / cm Hg / cm 2 / min, associated with average pore radii of less than 50 amperes, will be used for the pore radius value. On the other hand, membranes with very high permeabilities of up to 4000 × 10 -7 mole / cm Hg / cm 2 / min, associated with average pore radii, can be separated from gas or gas isotopes.

  at 200 A, will preferably be used for ultrafiltration or filtration in general.

13 2550953

Claims (16)

  1 o Process for producing a porous and permeable mineral membrane, characterized in that a thin layer of at least one peptised aluminum hydroxide gel is deposited on a porous permeable substrate, the membrane is dried, and obtained and then subjected to firing at a temperature of between 500 ° C. and 1100 ° C. The process according to claim 1, characterized in that the gel used consists of a hydroxide gel. of peptized aluminum.   3 Process according to claim 1, characterized in that the gel used consists of a gel of a mixed hydroxide of peptised aluminum capable of forming after pyrolysis. an aluminum spinel.   4. Process according to claim 3, characterized in that the gel used consists of a hydroxide gel.   mixed aluminum and peptized magnesium.   Process according to Claim 2, characterized in that the preparation of the peptised aluminum hydroxide gel is carried out by hydrolysis of an aluminum alkoxide and then peptisation of the hydrated aluminum oxide thus formed in the presence of a strong acid selected from the group comprising   hydrochloric acid and perchloric acid.   6. Process according to claim 3, characterized in that the preparation of a gel of a mixed hydroxide of peptised aluminum is carried out by hydrolysis of an aluminum alkoxide, addition to the solution obtained of a sodium salt. a chosen metal   in the group comprising magnesium, cobalt, copper, iron, manganese, nickel, and then peptization of the solution obtained in the presence of a strong acid selected from the group comprising hydrochloric acid and perchloric acid .   7 Process according to claim 3, characterized in that the preparation of a gel of a mixed hydroxide of peptised aluminum is carried out by hydrolysis of an aluminum alkoxide, peptization of the solution obtained in the presence of an acid strong selected from the group comprising hydrochloric acid and perchloric acid, then adding a salt of a metal selected from the group consisting of magnesium, cobalt, copper, iron, manganese, nickel. 14 2550953   Process according to any one of the claims   6 or 7, characterized in that the magnesium salt is constituted by magnesium acetate.   Process according to any one of the claims   6 or 7, characterized in that the magnesium salt is constituted by magnesium perchlorate.   Process according to any one of the claims   1 to 9, characterized in that the surface of the substrate on which the peptized gel layer is deposited has a pore radius of less than 2 microns.   Process according to Claim 10, characterized in that the substrate consists of a support having   These pores have radii of 4 to 20 microns, said support being covered with a thin layer having a pore radius of 0.05 to 2 microns.   Process according to any one of the claims   or 11, characterized in that the porous substrate is made of a ceramic material.   13. Process according to claim 12, characterized in that the porous substrate is of α-alumina.   Process according to any one of the claims   or 11, characterized in that the porous substrate is in one metal such as nickel.   Process according to any one of Claims 1 to 14, characterized in that the peptized gel layer is deposited on the substrate by coating.   16 Porous and Permeable Mineral Membrane   obtained by the process according to any one of claims 1 to 15.   17 Application of the membrane according to claim 16 to the isotopic separation of gas, filtration and ultrafiltration.